Resonance-type contactless power supply, integrated circuit and constant voltage controlling method therefor

ABSTRACT

The present disclosure relates to a resonance-type contactless power supply, an integrated circuit and a constant voltage control method. The resonance-type contactless power supply includes an inverter, a transmitter-side resonant circuit, a receiver-side resonant circuit, a rectifier circuit, and an output capacitance. In this resonance-type contactless power supply, the inverter receives electric energy, which is transferred to the rectifier circuit in a first state and is not transferred to the rectifier circuit in a second state. By switching between the first state and the second state, the resonance-type contactless power supply is controlled to provide a relatively constant voltage, and can be electrically coupled directly to a constant-voltage-type load.

CLAIM OF PRIORITY

This application is a divisional application of U.S. application Ser.No. 14/798,680, filed on Jul. 14, 2015, which published as U.S.2016/0013663 A1 on Jan. 14, 2016, and claims priority to ChineseApplication No. 201410335026.1, filed Jul. 14, 2015 (published as CN104079079 A), the contents of which are hereby incorporated byreference.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to the field of power electronics, andmore particularly, to a resonance-type contactless power supply, anintegrated circuit and a constant voltage control method.

Description of the Related Art

Contactless power supply is widely used in electronic products,especially in low-power electronic products such as cellular phones, MP3players, digital cameras, laptop computers, and the like, due to theirconvenience and availability. A conventional resonance-type contactlesspower supply typically has a resonance and magnetic coupling circuit,including a transmitting coil L1 and a receiving coil L2. Thetransmitting coil L1 and other components in a power transmitterconstitute a transmitter-side resonant circuit. The receiving coil L2and other components in a power receiver constitute a receiver-sideresonant circuit. Electric energy is transferred in a contactless mannerwhen the transmitter-side resonant circuit and the receiver-sideresonant circuit have the same resonance frequency. The receiver-sideresonant circuit is coupled to the transmitter-side resonant circuit byelectromagnetic field, and thus resonates when the transmitter-sideresonant circuit resonates. Typically, the above resonance frequency isreferred to as a self-inductance resonance frequency.

When operating in the self-inductance resonance frequency, theconventional resonance-type contactless power supply functions as acurrent source and provides a relatively constant current to a load.Thus, the resonance-type contactless power supply cannot be used for aload which needs a constant voltage.

BRIEF DESCRIPTION OF THE DISCLOSURE

In view of this, the present disclosure provides a resonance-typecontactless power supply, an integrated circuit and a constant voltagecontrol method for providing a relatively constant voltage, so that theresonance-type contactless power supply can be directly used for a loadwhich needs a constant voltage.

In a first embodiment, there is provided a resonance-type contactlesspower supply comprising:

an inverter configured to receive electric energy and output an ACcurrent with a self-inductance resonance frequency;

a transmitter-side resonant circuit comprising a transmitting coil forreceiving the AC current from the inverter;

a receiver-side resonant circuit comprising a receiving coil which isseparated from but electrically coupled to the transmitting coil in acontactless manner, and configured to receive electric energy from thetransmitting coil;

a rectifier circuit being electrically coupled to the receiver-sideresonant circuit;

an output capacitance being connected in parallel at an output of therectifier circuit;

a state switching circuit configured to control the receiver-sideresonant circuit to output the AC current to the rectifier circuit inthe first state, and to connect an input terminal of the rectifiercircuit to ground in the second state; and

a control circuit configured to switch the state switching circuitbetween the first state and the second state so that the rectifiercircuit outputs a constant output voltage.

Preferably, the state switching circuit comprises:

a first switch being electrically coupled between a first terminal ofthe input port of the rectifier circuit and ground;

a second switch being electrically coupled between a second terminal ofthe input port of the rectifier circuit and ground;

wherein the control circuit outputs a switching control signal inresponse to a feedback voltage which is in proportion to the outputvoltage of the rectifier circuit, for turning on or off the first switchand the second switch simultaneously.

Preferably, the control circuit increases an on time of the first switchand the second switch in each cycle when the feedback voltage increasesso as to decrease a time period of the first state, and decreases the ontime of the first switch and the second switch in each cycle when thefeedback voltage decreases so as to increase the time period of thefirst state.

Preferably, the control circuit comprises:

an error amplifier circuit configured to receive the feedback voltageand a reference voltage and to provide an error compensation signal;

a comparator configured to compare the error compensation signal with atriangular wave signal to provide a pulse-width modulation signal;

a driving circuit configured to provide the switching control signal forthe first switch and the second switch in response to the pulse-widthmodulation signal;

Preferably, the transmitting coil and the receiving coil are configuredto be coupled to each other in a predetermined coupling coefficient, andwhen operating in the self-inductance resonance frequency, a mutualinductance between the transmitting coil and the receiving coil is equalto an equivalent load impedance of a rated load in the first state.

In a second embodiment, there is provided a resonance-type contactlesspower supply comprising:

an inverter configured to receive electric energy and output an ACcurrent with a self-inductance resonance frequency in a first state, andto stop its operation in a second state;

a transmitter-side resonant circuit comprising a transmitting coil forreceiving the AC current from the inverter;

a receiver-side resonant circuit comprising a receiving coil which isseparated from but electrically coupled to the transmitting coil in acontactless manner, and configured to receive electric energy from thetransmitting coil;

a rectifier circuit being electrically coupled to the receiver-sideresonant circuit;

an output capacitance being connected in parallel at an output of therectifier circuit; and

a control circuit configured to switch the inverting circuit between thefirst state and the second state so that the rectifier circuit outputs aconstant voltage.

Preferably, the control circuit is configured to switch the invertercircuit between the first state and the second state in response to afeedback voltage, so as to decrease a time period during which theinverter circuit maintains in the first state when the feedback voltageincreases, and to increase the time period during which the invertercircuit maintains in the first state when the feedback voltagedecreases.

Preferably, the control circuit comprises:

an error amplifier circuit configured to receive the feedback voltagewhich is in proportion to an output voltage of the rectifier circuit anda reference voltage and to provide an error compensation signal;

a comparator configured to compare the error compensation signal with atriangular wave signal to provide a pulse-width modulation signal;

an inverter controller configured to switch between the first state andthe second state in response to the pulse-width modulation signal and toprovide an inverter control signal which has the self-inductanceresonance frequency in the first state and stops an operation of theinverter in the second state.

Preferably, the transmitting coil and the receiving coil are configuredto be coupled to each other in a predetermined coupling coefficient, andwhen operating in the self-inductance resonance frequency, a mutualinductance between the transmitting coil and the receiving coil is equalto an equivalent load impedance of a rated load in the first state.

In a third embodiment, there is provided an integrated circuit for aresonance-type contactless power supply, comprising:

a rectifier circuit;

a state switching circuit configured to control the receiver-sideresonant circuit to output the AC current to the rectifier circuit inthe first state, and to connect an input terminal of the rectifiercircuit to ground in the second state; and

a control circuit configured to switch the state switching circuitbetween the first state and the second state so that the rectifiercircuit outputs a constant output voltage.

Preferably, the state switching circuit comprises:

a first switch being electrically coupled between a first terminal ofthe input port of the rectifier circuit and ground;

a second switch being electrically coupled between a second terminal ofthe input port of the rectifier circuit and ground;

wherein the control circuit outputs a switching control signal inresponse to a feedback voltage which is in proportion to the outputvoltage of the rectifier circuit, for turning on or off the first switchand the second switch simultaneously.

Preferably, the control circuit increases an on time of the first switchand the second switch in each cycle when the feedback voltage increasesso as to decrease a time period of the first state, and decreases the ontime of the first switch and the second switch in each cycle when thefeedback voltage decreases so as to increase the time period of thefirst state.

Preferably, the control circuit comprises:

an error amplifier circuit configured to receive the feedback voltageand a reference voltage and to provide an error compensation signal;

a comparator configured to compare the error compensation signal with atriangular wave signal to provide a pulse-width modulation signal;

a driving circuit configured to provide the switching control signal forthe first switch and the second switch in response to the pulse-widthmodulation signal;

In a fourth embodiment, there is provided an integrated circuit for aresonance-type contactless power supply comprising:

an inverter configured to receive electric energy and output an ACcurrent with a self-inductance resonance frequency in a first state, andto stop its operation in a second state;

a control circuit configured to switch the inverting circuit between thefirst state and the second state so that the resonance-type contactlesspower supply outputs a constant output voltage.

Preferably, the control circuit is configured to switch the invertercircuit between the first state and the second state in response to afeedback voltage, so as to decrease a time period during which theinverter circuit maintains in the first state when the feedback voltageincreases, and to increase the time period during which the invertercircuit maintains in the first state when the feedback voltagedecreases.

Preferably, the control circuit comprises:

an error amplifier circuit configured to receive the feedback voltagewhich is in proportion to an output voltage of the rectifier circuit anda reference voltage and to provide an error compensation signal;

a comparator configured to compare the error compensation signal with atriangular wave signal to provide a pulse-width modulation signal;

an inverter controller configured to switch between the first state andthe second state in response to the pulse-width modulation signal and toprovide an inverter control signal which has the self-inductanceresonance frequency in the first state and stops an operation of theinverter in the second state.

In a fifth embodiment, there is provided a constant voltage controlmethod for a resonance-type contactless power supply comprising aninverter, a transmitter-side resonant circuit, a receiver-side resonantcircuit, a rectifier circuit and an output capacitor, comprising:

switching the resonance-type contactless power supply between the firststate and the second state so that the resonance-type contactless powersupply outputs a constant voltage,

wherein the inverter receives electric energy, which is transferred tothe rectifier circuit in a first state and is not transferred to therectifier circuit in a second state.

Preferably, a receiver-side resonant circuit outputs an AC current tothe rectifier circuit in the first state, and an input terminal of therectifier circuit is grounded in the second state.

Preferably, the inverter circuit receives electric energy and outputs anAC current with a self-inductance resonance frequency in the firststate, and the inverter stops its operation in the second state.

In this resonance-type contactless power supply, the inverter receiveselectric energy, which is transferred to the rectifier circuit in afirst state and is not transferred to the rectifier circuit in a secondstate. By switching between the first state and the second state, theresonance-type contactless power supply is controlled to provide arelatively constant voltage, and can be electrically coupled directly toa constant-voltage-type load.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the presentdisclosure will become more fully understood from the detaileddescription given hereinbelow in connection with the appended drawings,and wherein:

FIG. 1 is a schematic circuit diagram of an example resonance-typecontactless power supply according to a first embodiment of the presentdisclosure;

FIG. 2 is an equivalent circuit diagram of a resonance and magneticcoupling circuit in the example resonance-type contactless power supplyaccording to one embodiment of the present disclosure;

FIG. 3 is an equivalent circuit diagram of a resonance and magneticcoupling circuit in a decoupling state in the example resonance-typecontactless power supply according to one embodiment of the presentdisclosure;

FIG. 4 is a schematic diagram showing parameters of the equivalentcircuit in FIG. 3 when operating in a self-inductance resonancefrequency;

FIG. 5 is a simplified equivalent circuit diagram of a resonance andmagnetic coupling circuit in the example resonance-type contactlesspower supply according to one embodiment of the present disclosure;

FIG. 6 is a schematic diagram of an example resonance-type contactlesspower supply according to a first embodiment of the present disclosure;

FIG. 7 is a schematic circuit diagram of an example resonance-typecontactless power supply according to a second embodiment of the presentdisclosure; and

FIG. 8 is a flow chart of an example constant voltage control method fora resonance-type contactless power supply according to a thirdembodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

Reference will now be made in detail to particular embodiments of thedisclosure, it will be understood that the scope of the presentdisclosure is not limited to these embodiments. Furthermore, in thefollowing detailed description of the present disclosure, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present disclosure. However, it will be readilyapparent to one skilled in the art that the present disclosure may bepracticed without these specific details. In other instances, well-knownmethods, procedures, processes, components, and circuits have not beendescribed in detail so as not to unnecessarily obscure aspects of thepresent disclosure.

Furthermore, it will be understood by one skilled in the art thatattached drawings are to be regarded as illustrative, and may not bedrawn to scale.

Also, it will be understood in the following description that the term“circuit” refers to a conductive loop consisting of at least onecomponent or sub-circuit which are electrically coupled orelectromagnetically coupled to each other. When one component/circuit isreferred to as being “connected to” another component, or onecomponent/circuit is referred to as being “connected between” two nodes,it can be connected to or coupled to another component directly or withan intermediate component therebetween. The connection of two componentscan be physical or logical connection, or physical and logicalconnection. On the contrary, when one component is referred to as being“coupled directly to” or “connected directly to” another component,there will be no an intermediate component between two components.

Where the term “comprising” or “including” is used in the presentdescription and claims, it does not exclude other elements or steps,unless something otherwise is specifically stated. That is, it means“including, but not limited to”.

In the following description that the terms such as “first”, “second”and the like are used herein for purposes of description and are notintended to indicate or imply relative importance or significance. Theterm “plurality”, as used herein, is defined as two or more than two,unless something otherwise is specifically stated.

FIG. 1 is a schematic circuit diagram of an example resonance-typecontactless power supply according to a first embodiment of the presentdisclosure. As shown in FIG. 1, a resonance-type contactless powersupply 10 includes an inverter circuit 11, a transmitter-side resonantcircuit 12, a receiver-side resonant circuit 13, a rectifier circuit 14,an output capacitor C_(o), a state switching circuit 15 and a controlcircuit 16.

In this embodiment, the inverter circuit 11 and the transmitter-sideresonant circuit 12 constitute a power transmitter of the resonance-typecontactless power supply 10. The receiver-side resonant circuit 13, therectifier circuit 14, the output capacitor C_(o), the state switchingcircuit 15 and the control circuit 16 constitute a power receiver of theresonance-type contactless power supply 10.

The power transmitter and the power receiver are separated from butelectrically coupled to each other by the transmitter-side resonantcircuit 12 and the receiver-side resonant circuit 13 to transferelectric energy.

The inverter circuit 11 receives electric energy and outputs an ACcurrent V_(ac) with a self-inductance resonance frequency.

The inverter circuit 11 may be a full-bridge inverter circuit, ahalf-bridge inverter circuit, or other inverter circuit having similarfunctions.

The transmitter-side resonant circuit 12 includes a transmitting coil L1for receiving the AC voltage V_(ac) from the inverter circuit 11. Thetransmitter-side resonant circuit 13 needs an additionaltransmitter-side resonance capacitor C_(s) which is connected in seriesor in parallel with the transmitting coil L1 to provide a resonancecircuit. The transmitter-side resonance capacitor C_(s) is used forbalancing leakage inductance of the transmitter-side resonant circuit13, reflected inductance of the receiver-side resonant circuit 14 andparasitic inductance due to parasitic parameters of the circuit,eliminating voltage spike and surge current at a high frequency due tothe parasitic parameters of the circuit, suppressing electromagneticinterference and power supply noise so as to decrease apparent power ofthe power supply, and increasing power factor of the power supply.Obviously, one skilled in the art can understand that in some cases,distributed capacitance (for example, among wires of the transmittingcoil) of the circuit may be used as the transmitter-side resonancecapacitor so that an additional capacitor can be omitted in the circuit.

The receiver-side resonant circuit 13 includes a receiving coil L2. Thereceiving coil L2 is electrically coupled to the transmitting coil L2 inthe transmitter-side resonant circuit 12 in a detachable and contactlessmanner The receiver-side resonant circuit 13 receives electric energyfrom the transmitting coil L1.

Meanwhile, the receiver-side resonant circuit 13 needs an additionalreceiver-side resonant capacitor C_(d) for decreasing reactive power ata receiver-side and increasing active power transferred by the resonanceand magnetic coupling circuit. As mentioned above, distributedcapacitance (for example, among wires of the coil) of other componentsin the circuit may be used as the receiver-side resonant capacitor C_(d)so that an additional capacitor can be omitted in the circuit.

The transmitter-side resonant circuit 12 and the receiver-side resonantcircuit 13 constitute the resonance and magnetic coupling circuit.

FIG. 2 is an equivalent circuit diagram of a resonance and magneticcoupling circuit, i.e. a combination of a transmitter-side resonantcircuit 12 and a receiver-side resonant circuit 13, in the exampleresonance-type contactless power supply according to one embodiment ofthe present disclosure.

As shown in FIG. 2, the transmitting coil L1 is equivalent to a firstideal coil L_(s) and a coil resistor R_(s), and the receiving coil L2 isequivalent to a second ideal coil L_(d) and a coil resistor R_(d). Thefirst ideal coil L_(s) is coupled to the second ideal coil L_(d). InFIG. 2, the transmitter-side resonant circuit 12 and the receiver-sideresonant circuit 13 are each series resonance circuits. Thetransmitter-side resonant circuit 12 further includes a transmitter-sideresonance capacitor C_(s), and the receiver-side resonant circuit 13further includes a receiver-side resonant capacitor C_(d). As mentionedabove, the transmitter-side resonance capacitor C_(s) and thereceiver-side resonant capacitor C_(d) may be achieved by additionalcomponents or distributed parameters of other components.

Thus, the resonance and magnetic coupling circuit constitutes amutual-inductance coupling circuit.

Typically, the transmitter-side resonant circuit 12 and thereceiver-side resonant circuit 13 have the same resonance frequency sothat electric energy can be transferred in a resonant manner as follows,

f _(s)=½π·√{square root over (L _(s) ·C _(s))}=½π·√{square root over (L_(d) ·C _(d))}=f _(d)

wherein f_(s) is a resonance frequency of the transmitter-side resonantcircuit 12, f_(d) is a resonance frequency of the receiver-side resonantcircuit 13, L_(s) is an inductance value of the first ideal coil L_(s),L_(d) is an inductance value of the second ideal coil L_(d), C_(s) is acapacitance value of the transmitter-side resonance capacitor, and C_(d)is a capacitance value of the receiver-side resonant capacitor.

Preferably, the inductance value of the first ideal coil L_(s) may beset to be equal to the inductance value of the second ideal coil L_(d),and the capacitance value C_(s) of the transmitter-side resonancecapacitor may be set to be equal to the capacitance value C_(d) of thereceiver-side resonant capacitor so that the receiver-side resonantcapacitor 12 and the receiver-side resonant circuit 13 have the sameresonance frequency.

Typically, the above resonance frequency is referred to as aself-inductance resonance frequency. When operating at the aboveresonance frequency, the receiver-side resonant capacitor 12 and thereceiver-side resonant circuit 13 resonate simultaneously, andimpedances of inductors and capacitors in the resonance and magneticcoupling circuit are canceled out. The system efficiency is thusoptimized.

FIG. 3 is an equivalent circuit diagram of a resonance and magneticcoupling circuit in a decoupling state in the example resonance-typecontactless power supply according to one embodiment of the presentdisclosure. As shown in FIG. 3, because the coupling of the transmittingcoil L1 and the receiving coil L2 includes leakage inductance and mutualinductance, the resonance and magnetic coupling circuit as shown in FIG.2 can be equivalent to the circuit as shown in FIG. 3, where the idealcoils L_(s) and L_(d) are coupled to each other but represented here bytransmitter-side leakage inductance L_(s)′, receiver-side leakageinductance L_(d)′, and mutual inductance L_(M). Accordingly, theresonance and magnetic coupling circuit as shown in FIG. 2 may befurther equivalent to a two-port network as shown in FIG. 3.

FIG. 4 is a schematic diagram showing parameters of the equivalentcircuit in FIG. 3 when operating in a self-inductance resonancefrequency. As shown in FIG. 4, a series circuit of the transmitter-sideleakage inductance L_(s)′ and the transmitter-side resonance capacitorC_(s) has an equivalent impedance −jω₀L_(M) when the inverter circuit 11provides an AC voltage V_(ac) with a self-inductance resonance frequencyω₀ to the transmitter-side resonant circuit 12. Thus, the impedance ofthe mutual inductance can be canceled out. An input port of the powertransmitter has a minimized impedance, and the transmitter-side resonantcircuit resonates. Meanwhile, a series circuit of the receiver-sideleakage inductance L_(d)′ and the receiver-side resonant capacitor C_(d)has an equivalent impedance −Jω₀L_(M), so that an output port of thepower receiver has a minimized impedance, and the receiver-side resonantcircuit resonates.

Here, the system has a conversion efficiency η as follows,

$\eta = \frac{R_{L}}{{R_{s}\left\lbrack \left( \frac{R_{L} + R_{d}}{\omega_{0}L_{M}} \right)^{2} \right\rbrack} + R_{L} + R_{d}}$

wherein R_(L) is an equivalent load impedance of a rated load whenoperating in a first state. Assuming R_(s) has a value equal to that ofR_(d), the system has a conversion efficiency η with a maximum valuewhen ω₀L_(M)=R_(L). The transmitting coil L1 and the receiving coil L2have a relatively constant coupling coefficient in a normal operationstate. Inductance values of the transmitting coil L1 and the receivingcoil L2 are selected so that an impedance ω₀L_(M) of the mutualinductance between the transmitting coil L1 and the receiving coil L2 isequal to an equivalent load impedance R_(L) of a rated load in the firststate when the two coils are coupled to each other in a predeterminedcoupling coefficient, and when operating in the self-inductanceresonance frequency ω₀. Accordingly, the equivalent load impedance R_(L)is equal to ω₀L_(M) in the first state, which increases the conversionefficiency of the system.

FIG. 5 is a simplified equivalent circuit diagram of a resonance andmagnetic coupling circuit in the example resonance-type contactlesspower supply according to one embodiment of the present disclosure. Whenoperating in the self-inductance resonance frequency ω₀, the resonanceand magnetic coupling circuit of the resonance-type contactless powersupply 10 is equivalent to a current source A for subsequent rectifiercircuit 14, the output capacitor C_(o) and the load. The rectifiercircuit 14 performs only AC-DC conversion, but does not change anamplitude of the relevant voltage or current. Thus, the resonance-typecontactless power supply 10 functions as a current source for the loadif there is no the state switching circuit 15.

The rectifier circuit 14 is electrically coupled to the receiver-sideresonance circuit 13 for converting an AC current from the receiver-sideresonance circuit 13 to a DC current as an output.

The rectifier circuit 14 may be a full-bridge rectifier circuit or ahalf-bridge rectifier circuit.

The output capacitor C_(o) is connected in parallel at an output port ofthe rectifier circuit 14, for filtering the output DC current.

The state switching circuit 15 switches the resonance-type contactlesspower supply 10 between the first state and the second state. Theinverter circuit 11 receives electric energy, and transfers electricenergy to the rectifier circuit 14 in the first state and stopstransferring electric energy to the rectifier circuit 14 in the secondstate.

Specifically, the state switching circuit 15 is placed at the receiverside in this embodiment, for controlling the receiver-side resonantcircuit 13 to output an AC current to the rectifier circuit 14 in thefirst state, and to connect an input terminal of the rectifier circuit14 to ground in the second state.

The state switching circuit 15 may include a first switch S₁ and asecond switch S₂ for achieving its function, as shown in FIG. 1. Thefirst switch S₁ is connected between a first terminal of the input portof the rectifier circuit 14 and ground. The second switch S₂ isconnected between a second terminal of the input port of the rectifiercircuit 14 and ground. In the first state, the first switch S₁ and thesecond switch S₂ are both turned off so that the inverter circuit 11receives electric energy and transfers electric energy to the rectifiercircuit 14 by resonance as an output. In the second state, the firstswitch S₁ and the second switch S₂ are both turned on so that the inputport of the rectifier circuit 14 is grounded. The current at the inputport of the rectifier circuit 14 further flows to ground, instead of therectifier circuit 14 itself.

The control circuit 16 switches the state switching circuit 15 betweenthe first state and the second state so that the rectifier circuit 14outputs a constant voltage Vout.

Specifically, the control circuit 16 outputs a switching control signalQ in response to a feedback voltage V_(fb), for turning on or off thefirst switch S₁ and the second switch S₂ simultaneously.

In this embodiment, the feedback voltage V_(fb) may be obtained from theoutput voltage V_(out) of the rectifier circuit 14, i.e. the outputvoltage of the resonance-type contactless power supply, by a voltagedivision network. Thus, the feedback voltage V_(fb) is in proportion tothe output voltage V_(out).

FIG. 6 is a schematic diagram of an example resonance-type contactlesspower supply according to a first embodiment of the present disclosure.As shown in FIG. 6, the resonance and magnetic coupling circuit isequivalent to a current source A. The state switching circuit 15 isconnected to the input port of the rectifier circuit 14, i.e. an outputport of the current source A, so that the input port is grounded or in anormal state.

The control circuit 16 is electrically coupled to a control terminal ofthe state switching circuit 15. The control circuit 16 obtains acompensation signal V_(c) by calculating an error between the feedbackvoltage V_(fb) and a reference voltage V_(ref). The compensation signalV_(c) is compared with a triangular wave signal V_(ramp) to provide apulse-width modulation signal PWM. A switching control signal Q is thenobtained from the pulse-width modulation signal PWM, for turning on oroff the first switch S₁ and the second switch S₂ of the state switchingcircuit 15 simultaneously.

The control circuit 16 controls a ratio of a first time period duringwhich the state switching circuit 11 is in the first state and a secondtime period during which the state switching circuit 11 is in the secondstate, so that the rectifier circuit 14 outputs a constant voltageV_(out). In the first state, electric energy is transferred to therectifier circuit 14. In the second state, electric energy is nottransferred to the rectifier circuit 14, and an input voltage of therectifier circuit 14 is equal to 0. The output voltage of the rectifiercircuit is filtered and averaged by the output capacitor C_(o) to have arelatively constant output voltage V_(out).

The control circuit 16 may include an error amplifier circuit 16 a, acomparator CMP and a driving circuit DR.

The error amplifier circuit 16 a receives the feedback voltage V_(fb)and the reference voltage V_(ref) and to provide an error compensationsignal V_(c). The error amplifier circuit 16 a may include an erroramplifier EA and a compensation capacitor Cc. In this embodiment, aninverting input terminal and a non-inverting input terminal of the erroramplifier EA receive the feedback voltage V_(fb) and the referencevoltage V_(ref), respectively.

The comparator CMP compares the error compensation signal V_(c) and thetriangular wave signal V_(ramp) to provide the pulse-width modulationsignal PWM. The pulse-width modulation signal PWM has a duty ratio Dwhich varies in accordance with the error compensation signal V_(c) andhas a frequency equal to that of the triangular wave signal V_(ramp). Inthis embodiment, an inverting input terminal and a non-inverting inputterminal of the comparator CMP receive the error compensation signalV_(c) and the triangular wave signal V_(ramp), respectively.

It will be understood by one skilled person that the above input signalsmay be reversed if the control signal is defined in other manner. Forexample, the inverting input terminal and the non-inverting inputterminal of the comparator CMP receive the triangular wave signalV_(ramp) and the error compensation signal V_(c), respectively.

The driving circuit DR provides switching control signal Q for the firstswitch S₁ and the second switch S₂ in response to the pulse-widthmodulation signal PWM.

The control circuit 16 forms a voltage control loop to achieve negativefeedback. When the output voltage V_(out) increases, the feedbackvoltage V_(fb) increases so that the compensation signal V_(c)decreases. The pulse-width modulation signal PWM from the comparator CMPhas a low level when the triangular wave signal V_(ramp) is below thecompensation signal V_(c), and has a high level when the triangular wavesignal V_(ramp) is above the compensation signal V_(c). When thecompensation signal V_(c) decreases, the duty ratio D increases becausea time period of high level increases and a time period of low leveldecreases in a cycle of the pulse-width modulation signal. An on time ofthe first switch S₁ and the second switch S₂ in each pulse-widthmodulation cycle increases, and a time period during which the currentsource A supplies electric energy to the rectifier circuit 14 decreases.Consequently, electric energy per unit time, which is supplied to therectifier circuit 14, decreases, and the output voltage V_(out)decreases.

Instead, the control circuit 16 decreases the duty ratio of thepulse-width modulation signal PWM when the output voltage V_(out)decreases, so that electric energy per unit time which is supplied tothe rectifier circuit 14 increases and the output voltage V_(out)increases to maintain a constant output voltage.

The above embodiment is described in an example that the switchingcontrol signal Q from the driving circuit DR is used for turning on thefirst switch S₁ and the second switch S₂ when the pulse-width modulationsignal PWM has a high level. Alternatively, the switching control signalQ from the driving circuit DR is used for turning on the first switch S₁and the second switch S₂ when the pulse-width modulation signal PWM hasa low level. In such case, input terminals of the comparator may beexchanged, which is an equivalent of the above embodiment, as well knownby one skilled person.

Moreover, it will be understood by one skilled person that the controlcircuit as shown in FIG. 1 is given only as an example and can bereplaced by various types of conventional negative feedback voltagecontrol loops, as long as these control loops can adjust a duty ratio ofthe pulse-width modulation signal in response to a feedback voltage forcontrolling a ratio of a first time period in the first state and asecond time period in the second state to provide a constant outputvoltage.

Furthermore, the switching control signal Q has a frequency (i.e. thefrequency of the pulse-width modulation signal PWM) which should besmaller than a self-inductance resonance frequency, so that switchingoperation will not interfere with energy transfer between thetransmitter-side resonant circuit 12 and the receiver-side resonantcircuit 13.

Furthermore, the rectifier circuit 14, the state switching circuit 15and the control circuit 16 in the resonance-type contactless powersupply 10 according to this embodiment may be integrated as oneintegrated circuit. On the basis of the integrated circuit, the powerreceiver can be easily formed by adding peripheral components such asthe receiving coil, the receiver-side resonant capacitor, and the like.

The inverter receives electric energy, which is transferred to therectifier circuit in a first state and is not transferred to therectifier circuit in a second state. By switching between the firststate and the second state, the resonance-type contactless power supplyis controlled to provide a relatively constant voltage, and can beelectrically coupled directly to a constant-voltage-type load 18.

FIG. 7 is a schematic circuit diagram of an example resonance-typecontactless power supply according to a second embodiment of the presentdisclosure. As shown in FIG. 7, a resonance-type contactless powersupply 20 according to this embodiment includes an inverter 21, atransmitter-side resonant circuit 22, a receiver-side resonant circuit23, a rectifier circuit 24, an output capacitor C_(o) and a controlcircuit 25.

The transmitter-side resonant circuit 22, the receiver-side resonantcircuit 23, the rectifier circuit 24 and the output capacitor C_(o) arearranged and connected to each other in the same manner as in the firstembodiment.

However, this embodiment differs from the first and second embodiment inthat there is no a state switching circuit. The control circuit 25controls the inverter 21 to operate or to stop its operation, so thatelectric energy is or is not transferred to the rectifier circuit.

Specifically, the inverter 21 receives electric energy and outputs an ACcurrent with a self-inductance resonance frequency in a first state, andstops its operation in a second state.

The inverter 21 may be a full-bridge inverter, or a half-bridgeinverter. Preferably, the inverter 21 is a half-bridge inverter as shownin FIG. 7, including a first inverter switch S_(i1) and a second switchS_(i2). The first inverter switch S_(i1) is connected between a powerinput terminal and a first terminal of an output port of the inverter21. The second inverter switch S_(i2) is connected between the firstterminal and a second terminal of the output port of the inverter 21. Byturning on or off the first inverter switch S_(i1) and the secondinverter switch S_(i2), a DC current at the power input terminal can beconverted into an AC current with a frequency equal to that of aswitching frequency of the inverter.

The control circuit 25 switches the inverter circuit 21 between thefirst state and the second state to provide a constant output voltageV_(out) of the rectifier circuit 24, i.e. an output voltage of theresonance-type contactless power supply.

The control circuit 25 may include an error amplifier circuit 25 a, acomparator CMP and an inverter controller 25 b.

The error amplifier circuit 25 a receives a feedback voltage V_(fb) anda reference voltage V_(ref) and to provide an error compensation signalV_(c).

In this embodiment, the feedback voltage V_(fb), may be obtained fromthe output voltage V_(out) of the rectifier circuit 24, i.e. the outputvoltage of the resonance-type contactless power supply, by a voltagedivision network and a wireless communication circuit for transmitting arelevant signal V_(fb)′ from the power receiver to the powertransmitter. Thus, the feedback voltage V_(fb) is in proportion to theoutput voltage V_(out).

The comparator CMP compares the error compensation signal V_(c) with atriangular wave signal V_(ramp) to provide a pulse-width modulationsignal PWM.

The inverter controller 25 b switches between the first state and thesecond state in response to the pulse-width modulation signal PWM. Theinerter controller provides an inverter control signal which has theself-inductance resonance frequency in the first state and stops anoperation of the inverter in the second state. Preferably, the invertercontroller 25 b has an enable terminal for receiving the pulse-widthmodulation signal PWM, and operates in the first state (an operationstate) or in the second state (a non-operation state) in response to thepulse-width modulation signal PWM.

The inverter controller 25 b provides an inverter control signal with afrequency equal to a self-inductance resonance frequency in apredetermined manner when it operates. Thus, the inverter 21 provides anAC current and the transmitter-side resonant circuit 22 resonates, totransfer electric energy to receiver-side resonant circuit 23 and thento the rectifier circuit 24 as an output.

The inverter 21 does not provide an AC current when the invertercontroller 25 b stops operation. In such case, electric energy is nottransferred from the transmitter-side resonant circuit 22 to therectifier circuit 24.

The control circuit 25 forms a voltage control loop to achieve negativefeedback. When the output voltage V_(out) increases, the feedbackvoltage V_(fb) increases so that the compensation signal V_(c)decreases. The pulse-width modulation signal PWM from the comparator CMPhas a low level when the triangular wave signal V_(ramp) is below thecompensation signal V_(c), and has a high level when the triangular wavesignal V_(ramp) is above the compensation signal V_(c). As shown in FIG.7, an inverting terminal and a non-inverting terminal of the comparator25 a receive a triangular wave signal V_(ramp) and an error compensationsignal V_(c), respectively. When the compensation signal V_(c)decreases, the duty ratio decreases because a time period of low levelincreases and a time period of high level decreases in a cycle of thepulse-width modulation signal. An operation time of the inverter 21 ineach pulse-width modulation cycle decreases, and a time period duringwhich the inverter 21 supplies electric energy to the rectifier circuit24 decreases. Consequently, electric energy per unit time, which issupplied to the rectifier circuit 24, decreases, and the output voltageV_(out) decreases.

Instead, the control circuit 25 increases the duty ratio D of thepulse-width modulation signal when the output voltage V_(out) increases,so that electric energy per unit time which is supplied to the rectifiercircuit 24 increases and the output voltage V_(out) increases tomaintain a constant output voltage.

The above embodiment is described in an example that the invertercontroller is in an operation state (i.e. the first state) when thepulse-width modulation signal PWM has a high level. Alternatively, theinverter controller is in an operation state (i.e. the first state) whenthe pulse-width modulation signal PWM has a low level. In such case,input terminals of the comparator may be exchanged, which is anequivalent of the above embodiment, as well known by one skilled person.

Moreover, it will be understood by one skilled person that the controlcircuit as shown in FIG. 7 is given only as an example and can bereplaced by various types of conventional negative feedback voltagecontrol loops, as long as these control loops can adjust a duty ratio ofthe pulse-width modulation signal in response to a feedback voltage forcontrolling a ratio of a first time period in the first state and asecond time period in the second state to provide a constant outputvoltage.

Furthermore, the pulse-width modulation signal PWM has a frequency whichshould be smaller than a self-inductance resonance frequency, so thatswitching operation will not interfere with energy transfer between thetransmitter-side resonant circuit 22 and the receiver-side resonantcircuit 23.

Furthermore, the inverter circuit 21 and the control circuit 25 in theresonance-type contactless power supply 20 according to this embodimentmay be integrated as one integrated circuit. On the basis of theintegrated circuit, the power transmitter can be easily formed by addingperipheral components such as the transmitting coil, thetransmitter-side resonance capacitor, wireless signal receiver, and thelike.

In this resonance-type contactless power supply, the inverter receiveselectric energy and transfers it to the rectifier circuit in a firststate, and does not receive electrical energy or does not transfer it tothe rectifier circuit in a second state. By switching between the firststate and the second state, the resonance-type contactless power supplyis controlled to provide a relatively constant voltage, and can beelectrically coupled directly to a constant-voltage-type load.

This embodiment further reduces the number of components, and thusreduces circuit cost.

FIG. 8 is a flow chart of an example constant voltage control method fora resonance-type contactless power supply according to a thirdembodiment of the present disclosure. The resonance-type contactlesspower supply comprises an inverter, a transmitter-side resonant circuit,a receiver-side resonant circuit, a rectifier circuit and an outputcapacitor. As shown in FIG. 8, the method comprises the following steps:

switching the resonance-type contactless power supply between the firststate and the second state so that the resonance-type contactless powersupply outputs a constant voltage,

wherein the inverter receives electric energy, which is transferred tothe rectifier circuit in a first state and is not transferred to therectifier circuit in a second state.

A pulse-width modulation signal is used for switching control. Theoutput voltage maintains a constant value by adjusting the duty ratio ofthe pulse-width modulation signal.

In one preferable embodiment, a receiver-side resonant circuit outputsan AC current to the rectifier circuit in the first state, and an inputterminal of the rectifier circuit is grounded in the second state.

In another preferable embodiment, the inverter circuit receives electricenergy and outputs an AC current with a self-inductance resonancefrequency in the first state, and the inverter stops its operation inthe second state.

In this resonance-type contactless power supply, the inverter receiveselectric energy, which is transferred to the rectifier circuit in afirst state and is not transferred to the rectifier circuit in a secondstate. By switching between the first state and the second state, theresonance-type contactless power supply is controlled to provide arelatively constant voltage, and can be electrically coupled directly toa constant-voltage-type load.

The foregoing descriptions of specific embodiments of the presentdisclosure have been presented, but are not intended to limit thedisclosure to the precise forms disclosed. It will be readily apparentto one skilled in the art that many modifications and changes may bemade in the present disclosure. Any modifications, equivalence,variations of the preferred embodiments can be made without departingfrom the doctrine and spirit of the present disclosure.

What is claimed is:
 1. A resonance-type contactless power supplycomprising: an inverter configured to receive electric energy and outputan AC current with a self-inductance resonance frequency in a firststate, and to stop its operation in a second state; a transmitter-sideresonant circuit comprising a transmitting coil for receiving said ACcurrent from said inverter; a receiver-side resonant circuit comprisinga receiving coil which is separated from but electrically coupled tosaid transmitting coil in a contactless manner, and configured toreceive electric energy from said transmitting coil; a rectifier circuitbeing electrically coupled to said receiver-side resonant circuit; anoutput capacitance being connected in parallel at an output of saidrectifier circuit; and a control circuit configured to switch saidinverting circuit between said first state and said second state so thatsaid rectifier circuit outputs a constant voltage.
 2. The resonance-typecontactless power supply according to claim 1, wherein said controlcircuit is configured to switch said inverter circuit between said firststate and said second state in response to a feedback voltage, so as todecrease a time period during which said inverter circuit maintains insaid first state when said feedback voltage increases, and to increasesaid time period during which said inverter circuit maintains in saidfirst state when said feedback voltage decreases.
 3. The resonance-typecontactless power supply according to claim 1, wherein said controlcircuit comprises: an error amplifier circuit configured to receive saidfeedback voltage which is in proportion to an output voltage of saidrectifier circuit and a reference voltage and to provide an errorcompensation signal; a comparator configured to compare said errorcompensation signal with a triangular wave signal to provide apulse-width modulation signal; and an inverter controller configured toswitch between said first state and said second state in response tosaid pulse-width modulation signal, and to provide an inverter controlsignal which has said self-inductance resonance frequency in said firststate and stops an operation of said inverter in said second state. 4.The resonance-type contactless power supply according to claim 1,wherein said transmitting coil and said receiving coil are configured tobe coupled to each other in a predetermined coupling coefficient, andwhen operating in said self-inductance resonance frequency, a mutualinductance between said transmitting coil and said receiving coil isequal to an equivalent load impedance of a rated load in said firststate.
 5. An integrated circuit for a resonance-type contactless powersupply comprising: an inverter configured to receive electric energy andoutput an AC current with a self-inductance resonance frequency in afirst state, and to stop its operation in a second state; and a controlcircuit configured to switch said inverting circuit between said firststate and said second state so that said resonance-type contactlesspower supply outputs a constant output voltage.
 6. The integratedcircuit according to claim 5, wherein said control circuit is configuredto switch said inverter circuit between said first state and said secondstate in response to a feedback voltage, so as to decrease a time periodduring which said inverter circuit maintains in said first state whensaid feedback voltage increases, and to increase said time period duringwhich said inverter circuit maintains in said first state when saidfeedback voltage decreases.
 7. The integrated circuit according to claim5, wherein said control circuit comprises: an error amplifier circuitconfigured to receive a feedback voltage which is in proportion to anoutput voltage of said resonance-type contactless power supply and areference voltage and to provide an error compensation signal; acomparator configured to compare said error compensation signal with atriangular wave signal to provide a pulse-width modulation signal; andan inverter controller configured to switch between said first state andsaid second state in response to said pulse-width modulation signal andto provide an inverter control signal which has said self-inductanceresonance frequency in said first state and stops an operation of saidinverter in said second state.
 8. The constant voltage control methodaccording to claim 5, wherein said inverter circuit receives electricenergy and outputs an AC current with a self-inductance resonancefrequency in said first state, and said inverter stops its operation insaid second state.